Molecular Dynamics Simulation of Microwelds Formation and Breakage During Ultrasonic Copper Wire Bonding

摘要

Nowadays ultrasonic (US) copper wire bonding gests more required and applied in power electronics. Despite its large amounts of usage, the underlying bonding mechanisms are still unclear. Among them, the dynamic changes of microwelds are essential to the bonding process as the bonding quality and reliability are greatly influenced by the formed microwelds. In this work, the formation and breakage of microwelds during US copper wire bonding are analyzed by molecular dynamics simulation. Due to the limit of the computational expense, a small local interface consisting of ~40000 atoms is simulated. In the model, the copper substrate is fixed while the movement of the copper wire is imposed. Microwelds are first formed during the downwards moving of the wire and get enlarged with further vertical displacement. The formed microwelds can be broken due to the vibration while new microwelds can be formed in the meantime. Because of the formation, deformation and breakage of the microwelds, the surface roughness can be significantly changed and the vertical displacement is the most influential factor. Defects caused by the microwelds formation and breakage can be clearly observed in the simulation results. The achieved information has a high potential to enhance the bonding quality and reliability.